It is well known that the geometry, for example the shape, size and position, of the blades of a rotor of a turbo machine has a significant effect on the performance and efficiency of the machine.
According to the present invention, there is provided a rotor arrangement for a turbo machine which rotor arrangement comprises an annular series of spaced primary blades mounted for rotation on a shaft, and an annular series of spaced secondary blades, also mounted for rotation on said shaft, at least part of each of the secondary blades being disposed between a successive pair of primary blades, so as to effect at least partial axial overlap between the two series of blades, the arrangement being such that the series of secondary blades is movable relative to the set of primary blades between two predetermined end positions.